1. Field of the Invention
The present invention relates to immunological procedures for determining and/or detecting the presence or amount of an immunologically reactive analyte such as a ligand or ligand receptor in an aqueous phase sample. In particular, the invention relates to improved materials and methodology for detecting the presence of hormonal analytes such as human chorionic gonadotropin (hCG) and/or human luteinizing hormone (hLH) in urine, the presence of such hormonal analytes being indicative of conditions such as pregnancy and of phases in the female menstrual cycle. In another aspect, the invention relates to improved materials and methodology for use in connection with the metal sol capture immunoassay procedures and kits disclosed in co-assigned U.S. application Ser. No. 105,285, filed Oct. 7, 1987 (now U.S. Pat. No. 4,859,612), the entirety of the disclosure of which is hereby specifically incorporated by reference. Additionally, the disclosure of the '285 application provides an excellent description of prior developments in the field of diagnostic procedures based on immunochemistry and reactions.
2. Description of Prior Activities and Developments
In accordance with certain specific procedures disclosed in said '285 application, antibody coated gold sol particles and antibody coated solid phase particles are dispersed in an aqueous system containing human urine. The antibodies are respectively and specifically immunoreactive with respect to different epitopes on a searched for analyte in the urine, and if such analyte is present, the respective antibodies will immunoreact therewith to form a collectible, solid phase, gold particle containing immunocomposite which may then be collected on a filter element mounted in a suitable collection device. Such collection devices are the subject of another co-assigned, U.S. application Ser. No. 107,240, filed Oct. 13, 1987 (now U.S. Pat. No. 4,999,163). The entirety of the disclosure of the '240 application is also specifically incorporated herein by reference. The collected gold sol particle containing composite has a distinctive pink to purplish coloration that is readily visually detected upon observation with the naked eye. The intensity of the coloration of the composition, generally speaking, is directly related to the amount of analyte that is present in the sample.
In the past, false positive readings have sometimes been the result when procedures such as those disclosed in the '285 application were used to test for hCG or hLH. The exact causation for such false readings is not completely understood; however, it is believed that the false positive readings are the result of several separate phenomena. Firstly, human urine contains certain sedimentation which may tend to clog the pores of the collection filter and prevent, or at least inhibit flow of the aqueous reaction phase through the filter. Thus, gold particles carrying antibodies which have not reacted to form an immunocomposite may be prevented from flowing through the filter and as a result will be non-specifically present on the filter even after washing to exhibit the pinkish to purplish coloration that is the inherent characteristic of the gold sol particle. Secondly, collection filter membranes of the type utilized in connection with the present invention sometimes have a tendency to non-specifically bind unreacted antibody so as to retain unreacted gold sol particles on the collection membrane. Thirdly, certain substances in urine may act to increase the tendency of the collection filter element to non-specifically bind unreacted immunoreactive substances. Additionally, the pinkish to purplish environment that surrounds the test materials and reaction phase may provide an optical impression that persists to cause an uncolored collection filter to appear slightly pink to an untrained eye, even after washing, and thus the test may provide a false appearance of being slightly positive or at least an appearance that is confusing.
The presence of contamination in urine has been addressed previously in "Principles of Biochemistry", White, Handler, Smith, Hill Lehman, 6th Edition, McGraw-Hill, at page 1077, where the contaminants are described as consisting of nucleoproteins or microproteins together with some epithelial cells. Such phenomena has also been recognized in U.S. Pat. Nos. 3,873,682 and 4,270,923. However, in none of these prior disclosures is there any mention that such contaminants might interfere with an immunoassay procedure by clogging a collection filter, by enhancing the tendency for the filter to bind non-specifically with immunoreactive substances, or by otherwise interfering with the filtration operation. Rather, in the case of both such prior patents, the urine contaminants caused a turbidity which interfered with the agglutination procedure employed, and in each case a specific solid contact material was used, hopefully to remove the turbidity causing materials without disturbing the analyte content of the urine. However, these and other attempts to remove undesirable impurities from urine samples have sometimes resulted in removal also of the analyte that is to be determined and/or detected, thus foiling the entire procedure.